A media content provider or distributor may stream media contents to streaming clients, which may take the form of various user end devices, such as televisions, notebook computers, and mobile handsets. A media content may comprise a Media Presentation Description (MPD) and a plurality of media segments, which may be carried in a media stream. The MPD may be an extensible markup language (XML) file or document describing the media content, such as its various representations, Uniform Resource Locator (URL) addresses, and other characteristics. For example, the media content may comprise several media components (e.g. audio, video, and text), each of which may have different characteristics that are specified in the MPD. Each media component comprises a plurality of media segments containing the parts of actual media content, and the segments may be stored collectively in a single file or individually in multiple files. Each segment may contain a pre-defined byte size (e.g., 1,000 bytes) or an interval of playback time (e.g., 2 or 5 seconds) of the media content.
Media content may be delivered from a streaming server to a streaming client adaptively based on a variety of factors, such as network conditions, device capability, and user choice. Upon reception of the TS, the streaming client may parse the TS to extract information from within. Adaptive streaming technologies may include various technologies or standards implemented or being developed, such as Dynamic Adaptive Streaming over Hypertext Transfer Protocol (HTTP) (DASH), HTTP Live Streaming (HLS), Adaptive Transport Streaming (ATS), or Internet Information Services (IIS) Smooth Streaming.
For example, as one type of adaptive streaming, DASH has been defined by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) in an international standard. The standard, usually identified as ISO/IEC 23009-1, is entitled “Information technology—Dynamic adaptive streaming over HTTP (DASH)—Part 1: Media presentation description and segment formats” and incorporated herein by reference. Recent amendments to the ISO/IEC 23009-1 have provided a way of transporting event messages (denoted as emsg) using an ISO-Base Media File Format (BMFF) box. The emsg box may be specific to ISO-BMFF media segments, and there may be no generic counterpart to the emsg event in the media segments of a transport stream (TS) defined by the Moving Picture Experts Group-2 (MPEG-2) standard. Consequently, adaptive streaming may not be conveniently delivered to user devices with MPEG-2 TS support.